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Help with Plaster Stains

Love TFP! First time posting. This is second pool season using BBB method, third season with this older pool. I have brown staining all over the bottom of the pool. They were there when we took off the pool cover in early May. Seemed to get worse when we did the first shock of the season, but maybe we could just see them better.
Pool water is sparkly and clear. Use Clorox for disinfecting. Added polyquat 60 before closing last fall, otherwise no other type of algaecide for a year. Two seasons ago used the Leslie's stuff for black and mustard algae in August and at closing. We had some plaster stains two seasons ago when we bought the house, but nothing like this. I've attached pics.

FC 5.5
CC 0
pH 7.8
TA 70
CH 270
CYA 40

Constantly adding MA to keep pH below 8.0. And just had a spell when I had to keep adding calcium, as the CH suddenly dropped below 250.

Re: Help with Plaster Stains

Hey Bama,
After a couple hours with a trichlor puck, no difference. But the black stain caused by the vitamin c sock has now disappeared, and the same area is now noticeably more white. Now what? Does that mean all the stains are from the copper algaecide we used more than two years ago? I dread an AA treatment because the pool's pH is always high, and the process seems very complicated.